Manufacture of artificial stone.



Uwrrnn Sterne ATENT rrrcn.

VVI LHELM SCHWARZ, OF ZURICH, SWITZERLAND.

MANUFACTURE OF ARTIFICIAL STONE.

SPECIFICATION forming part of Letters Eatent NO. 670,299, dated March19, 1901.

Application filed October 6, 1899. Serial No. 732,817. (N0 p m n -l Toall whom it may concern:

Be it known that I, WILHELM ScHwARz, a citizen ofSwitzerland,residing atNo. 46 VVeinbergstrasse, Zurich, Switzerland, have invented a new anduseful Improvement in the Manufacture of Artificial Stone, of which thefollowing is a specification.

My invention relates to the manufacture of artificial stones forbuilding and other purposes, and in particular to the production ofartificial calcareous sandstones. The manu facture of this character ofartificial stone had not prior to my invention reached that state ofdevelopment where it was possible to obtain a product of uniformcharacter and of reliable strength and durability. Under the old methodsthere remained always an element of uncertainty as to the quality of theproduct resulting from each operation, and it was impossible to supplythe market with building materials of fixed ratings.

It is one of the objects of my invention to eliminate this uncertaintyfrom the manufacture of artificial stones of the character described andto enable the manufacturer to furnish products of a fixed and invariablecharacter and of the greatest possible amount of strength anddurability.

With this and other objects in view my invention consists in the method,steps, and features hereinafter described, and more par ticularlypointed out in the claims.

In the course of my experiments and researches in this direction I havefound that the principal cause of failure to produce a satisfactoryartificial calcareous sandstone consists in the varying conditions and.states of moisture of the sand employed for this purpose, the sand beingtoo moist at times and at others too dry. Sometimes the mixture of sandand lime is a wet and pulpy mass which is badly suited to being pressedor molded, while at others the opposite difficulty occurs that is tosay, the mixture contains an insufficient amount of moistu re tocompletely slake the lime-in consequence of which the mass afterhardening receives rents and fissures and generally deteriorates inconsequence of the after-slaking. Owing to the natural moistureordinarily existing in sand and to the combined action of this moistureand that of the atmosphere a chemical combination bemoisture in the formof water or steam which must be added to insure the completion of theconversion of the lime into the silicate of calcium, the binding andhardening medium. This conversion must be complete when the last amountof moisture has been used up, for the reasons explained above. In otherwords, the quantity of moisture should be neither too great nor toosmall, because in either case an unsatisfactory product is obtained.This objection can be avoided only if means are offered whereby thequantity of moisture already present or to be added can be ascertainedor computed beyond a peradventure, and thus the operator is enabled tostart the process from a constant and fixed point. According to myinvention this starting-point for the process is reached in anexceedingly simple manner by completely drying the sand and preferablyalso the lime before they are mixed and before the necessary moisturefor silicatization is added. Indeterminable quantities of moisture orwater are thereby completely avoided and eliminated from the process,which may now be carried out with accurately determinable and certainquantities. The effect of the process is thus made absolutely certainand depends no longer on the skill and practical experience of theoperator,but solely on calculation, the result being a calcareoussandstone of unvarying quality and homogeneity. Such result, moreover,was hitherto impossible of realization, even at the hands of highlyskilled and experienced manipulators.

In carrying out my invention a certain quantity of sand-say one hundredparts, by weight-is dried by means of heat in vacuo, preferably in avacuum-pan provided with revoluble wings or other means for subsequentlymixing the sand with the other ingredients. I prefer a vacuum apparatusto other means of drying, because I find that more economical, and forthe further and very important reason that by drying in vacuo no air canhave access to the sand. By preventing access of air no carbonic dioxid,which is always contained in the air, can come in contact with thematerials to be mixed, which is results in the removal of the air in theinterstices of the sand, which air contains moisture and, moreover,would interfere with the formation of silicate of lime by preventing theotherwise more intimate con tact between the lime and sand. After thesand has been completely dried I add. thereto about two parts, byweight, of powdered or comminuted lime, which has preferably beencompletely dried previously, and the two substances are then completelymined under the vacuum, whereupon moisture or water, preferably in theform of steam, is added and mixed with the sand and lime until theformat-ion of the silicate of lime is complete.

Heating of the sand for the purpose of drying the same not only enablesthe process to start from a constant point, but it also opens upthesilicic acid of the sand. The vacuum, which is maintained during all thestages of the process, prevents the access of carbonic acid or carbondioxid to the lime,which would result in the formation of calciumcarbonate, and hence seriously interfere with the combination of thesilicic acid with the lime to form the necessary binding material-thesilicate of lime. By introducing the water as steam the danger ofintrodi'lcing the carbonic acid with the moisture is avoided, and thusall avenues of access of the carbonic acid are cut oif under thepreferred embodiment of my invention.

The lime, while preferably dried, need in general not undergo specialdrying operations, because, in the first place, it is normallysufficiently dry,and,in the second place, its percentage of moisturebears a very insignificant ratio to the amount of moisture contained inthe sand, as will appear from a consideration of the followingexample,taken from an actual working of the process: If we take onehundred kilograms of sand and allow for the same ten per cent. ofmoisture,

which is a reasonable estimate, borne out by practice, the same willcontain ten thousand grams of water. If to this are then added twokilograms of lime, the amount usually required, and allowing for thesame as much as five per cent. of moisture, the entire quantity of watercontained in thelime would only amount to one hundred grams. This amountis so small that it plays a very unimportant part as compared with themoisture contained in the sand, and since the water contained in limeusually is much less than given above it may be safely neglected withoutmaterially interfering with the calculation of the moisto re to be addedto the dried sand to obtain a product of uniform quality.

What I claim, and desire to secure by Letters Patent, is-

1. The process of making artificial stone which consists in completelydrying the sand in vacuo, then adding lime to the dried sand and mixingin vacuo and adding moisture thereto. 1

The process of making artificial sandstone, which' consists incompletely drying sand in vacuo, then adding dried lime thereto andmixing the ingredients in cacao-and adding moisture thereto.

3. The process of making artificial sandstone, which consists in dryingthe sand by heat in 'vacuo, then adding lime to the dried sand anddrying the lime, then mixing the whole and adding moisture all whileunder a vacu u m.

4. The process of making artificial sandstone, which consists in heatingsand under a vacuum until completely dry, then adding dried lime, andmixing both substances while maintaining the vacuum, and then add ing tothe mixture a predetermined quantity of moisture and again mixing allunder a vacuum.

5. The process of preparing artificial sandstone, which consists inheating sand under a vacuum until completely dried, then adding theretolime, then mixing in cacao, then introd ucing a predetermined quantityof steam to the mixture and again mixing all in vacuo.

In witness whereof I have hereunto set my hand in presence of twowitnesses.

\VILHELM SOHVVARZ.

Witnesses:

WM. WoFFLEns, ALFRED BAERWOLFF.

